This week, a former Japanese official has confirmed, perhaps for the first time, “that past administrations… gave tacit approval to letting U.S. vessels and aircraft carrying atomic weapons to pass through or stop over in Japan,” reports the Japan Times.

That’s a problem for two reasons: Past governments in Japan having consistently denied the existence of the covert pact. If true, the revelation could possibly strain ties. Second, the DPJ campaigned on a platform of exposing the purported secret nuclear pact. Now that the news appears to be out, the DPJ has fodder with which to challenge the Obama administration.

It appears more a matter of principle than practicality. It’s not as if US warships or planes are landing in Japan with nuclear weapons. As the Japanese former official clarified, “a U.S. ship carrying nuclear weapons has not made a port call in Japan since the end of the Cold War.”

How the US and the DPJ will respond to this news is not yet clear. So far, a White House press release said that in a phone call early Thursday, Obama and Hatoyama "stressed the importance of a strong U.S.-Japan alliance and their desire to build an even more effective partnership," reports Japan Today.

Hatoyama in the past supported calls to remove Futenma air base -- long a source of friction as it lies in a crowded urban area -- out of Okinawa. A plan between the two countries would shift the Marine base's facilities to reclaimed land on a quiet part of the island.

Kevin Maher, who heads the Japan desk at the State Department, said that a realignment deal reached with a previous government on Okinawa -- under which 8,000 Marines would head to the US territory of Guam by 2014 -- was final.

The Associated Press has said the issue “will likely be the first test of its leader's efforts to remake the country's relationship with Washington while maintaining their strong alliance."The DPJ may also pull back its support for US efforts in Afghanistan, AFP reports:

The party, while in opposition, criticised moves by the more hawkish LDP governments in supporting "American wars," and has said it would end next year a naval refuelling mission supporting US-led operations in Afghanistan.